In the formation of photosensitive silver halide emulsions, the physical ripening or growing step during which time the silver halide grains increase in size is considered important. During the ripening stage an adequate concentration of a silver halide solvent, for example, excess halide, generally bromide, is employed which renders the silver halide much more soluble than it is in pure water because of the formation of complex ions. This facilitates the growth of the silver halide grains. While excess bromide and ammonia are the most common ripening agents, the literature also mentions the use of water-soluble thiocyanate compounds as well as a variety of amines in place of bromide. See, for example, Photographic Emulsion Chemistry, G. F. Duffin, The Focal Press London, 1966, page 59.
The art has also disclosed the employment of a water-soluble thiocyanate compound during the formation of the grains, that is, during the actual precipitation of the photosensitive silver halide. For example, U.S. Pat. No. 3,320,069 discloses a water-soluble thiocyanate compound which is present as a silver halide grain ripener either during precipitation of the light-sensitive silver halide or added immediately after precipitation. The precipitation of the silver halide grains in the aforementioned patent is carried out, however, with an excess of halide.
U.S. Pat. No. 4,406,576 is directed to a method for the continuous formation of photosensitive siliver halide emulsions wherein a silver salt is reacted with a halide salt in the presence of gelatin to form a photosensitive silver halide emulsion and said formation takes place in the presence of a sulfur-containing silver halide grain ripening agent, such as a water-soluble thiocyanate compound, and the thus-formed silver halide emulsion is continuously withdrawn from the reaction chamber while silver halide grain formation is occurring. During precipitation the halide concentration in the reaction medium is maintained at less than 0.010 molar. The patent states that is is known in the art to prepare silver halide grains in the presence of an excess of silver ions. The patent relates to such a precipitation with the additional steps of continually adding the sulfur-containing ripening agent and continually withdrawing silver halide grains as they are formed.
U.S. Pat. No. 4,150,994 is directed to a method of forming silver iodobromide or iodochloride emulsions which are of the twinned type which comprises the following steps:
(a) forming a monosized silver iodide dispersion;
(b) mixing in the silver iodide dispersion aqueous solutions of silver nitrate and alkali or ammonium bromides or chlorides in order to form twinned crystals;
(c) performing Ostwald ripening in the presence of a silver solvent, such as ammonium thiocyanate, to increase the size of the twinned crystals and dissolve any untwinned crystals;
(d) causing the twinned crystals to increase in size by adding further aqueous silver salt solution and alkali metal or ammonium halide; and
(e) optionally removing the water-soluble salts formed and chemically sensitizing the emulsion.
Copending application of Arther M. Gerber, Ser. No. 194,561, filed Oct. 6, 1980 (commonly assigned) is directed to a method for forming narrow grain size distribution silver halide emulsions by the following steps:
1. Forming photosensitive silver halide grains in the presence of a water-soluble thiocyanate compound with a halide/silver molar ratio ranging from not more than about 5% molar excess of halide to not more than about a 25% molar excess of silver; and
2. Growing said grains in the presence of said water-soluble thiocyanate compound for a time sufficient to grow said grains to a predetermined grain size distribution.
Copending application of Edwin H. Land, Ser. No. 234,937, filed Feb. 17, 1981, (commonly assigned) is directed to a method for forming a predetermined spaced array of sites and then forming single effective silver halide grains at said sites. Thus, by forming the sites in a predetermined spatial relationship, if the silfver halide grains are formed only at the sites, each of the grains will also be located at a predetermined and substantially uniform distance from the next adjacent grain and their geometric layout will conform to the original configuration of the sites.
The term, "single effective silver halide grain," refers to an entity at each site which functions photographically as a single unit which may or may not be entire unit can participate in electronic and ionic processes such as latent image formation and development.
Copending application Ser. No. 234,937 discloses one method for forming sites by exposing a photosensitive material to radiation actinic to said photosensitive material and development the so-exposed photosensitive material to provide sites for the generation of silver halide corresponding to the pattern of exposure and then forming photosensitive silver halide grains at the sites. In a preferred embodiment, the sites are provided by the predetermined patterned exposure of the photoresist whereby upon development of the exposed photoresist a relief pattern is obtained wherein the peaks or valleys comprise the above described sites.
While the single effective silver halide grains may be formed employing the described photoresist relief pattern, it is preferred to replicate the relief pattern by conventional means, example, by using conventional electroforming techniques to form an embossing master from the original relief image and using the embossing master to replicate the developed photoresist pattern in an embossable polymeric material.
Copending application of Arthur M. Gerber, Ser. No. 298,640 filed concurrently herewith, (common assignee) is directed to a method for forming a photosensitive element comprising a plurality of single effective silver halide grains, which method comprises coalescing fine-grain silver halide in a plurality of predetermined spaced depressions. Preferably, the coalescence is effected by contacting fine-grain silver halide with a solution of a silver halide solvent.
Copending application of Edwin H. Land and Vivian K. Walworth, Ser. No. 298,638, filed concurrently herewith, (common assignee) is directed to a method of forming a photosensitive element comprising a plurality of single effective silver halide grains, which method comprises coalescing a fine-grain emulsion in a plurality of predetermined spaced depressions by contacting said fine-grain emulsion with a solution of a silver halide solvent containing a dissolved silver salt.